Disable remote lifecycle logging from Akka.

This changes the default setting to `off` for remote lifecycle events. When this is on, it is very chatty at the INFO level. It also prints out several ERROR messages sometimes when sc.stop() is called.

core/src/main/scala/spark/util/AkkaUtils.scala

@@ -37,7 +37,7 @@ private[spark] object AkkaUtils {
       akka.stdout-loglevel = "ERROR"
       akka.actor.provider = "akka.remote.RemoteActorRefProvider"
       akka.remote.transport = "akka.remote.netty.NettyRemoteTransport"
-      akka.remote.log-remote-lifecycle-events = on
+      akka.remote.log-remote-lifecycle-events = off
       akka.remote.netty.hostname = "%s"
       akka.remote.netty.port = %d
       akka.remote.netty.connection-timeout = %ds